Bubblers are used in a variety of industries to supply gaseous chemicals. Typically, the bubbler includes a carrier gas inlet tube that is immersed in a liquid chemical. The tube usually has a single gas outlet positioned near the bottom level of the liquid chemical so that a single stream of carrier gas bubbles through the liquid chemical. Some of the liquid chemical is vaporized by the carrier gas to form the gaseous chemical.
In the semiconductor industry, bubblers are used to provide a variety of gaseous chemicals for semiconductor fabrication and processing. For example, bubblers are used to provide chemicals such as gaseous trichlorosilane for epitaxial deposition of single crystal silicon. The standard bubbler system used in the industry is a dual bubbler system. The dual bubbler system utilizes two bubblers that operates as a batch process. That is, one bubbler is the lead and the other is the lag bubbler. The lag bubbler is used first, and when the weight of the liquid in the lag bubbler drops to a certain level, it is taken off line and is being replaced with a filled new bubbler. However, the role of lead and lag bubbler is reversed following the bubbler replacement. The empty bubbler is sent to a chemical company for subsequent cleaning and filling with liquid chemical.
The dual bubbler system has many limitations. It is expensive to operate, being prone to high maintenance and material costs. Environmental costs are required to dispose of residual chemical in the system after each batch. The dual system increases exposure to chemical hazards since the system must be dismantled and cleaned. Cycle times of the system are increased since the dual bubbler system must be taken off line at the end of its batch. Moreover, the dual bubbler system has performance limitations. Contaminants concentrate in the bottom of the lag bubbler and can be carried out into the semiconductor system and increase the risk of process contamination. Further, as the liquid level drops during batch operation of the dual bubbler system, certain bubbler components comprised of metal, such as iron, can leach into the chemical liquid and such metals can be carried out and contaminate the semiconductor process. Thus, it is desirable to provide a bubbler system which is not subject to the foregoing limitations.